1. Field of the Invention
Proteases or peptidases have a wide range of activities, functions and specificities in vivo. The need to produce various polypeptides for specific functions, while controlling their lifetime is an important function of peptidases. Peptidases also serve to process various proteins, whereby leader sequences may be removed, hormones or other active polypeptides excised from a larger polypeptide or the like. An alternative method for controlling the enzymatic activity at a particular site or in a medium in a host is the production of a specific enzyme inhibitor. This strategy is employed with human leukocyte elastase, a serine protease. Leukocyte elastase is involved in the phagocytosis of pathogens in the lungs. Failure to inhibit the enzyme, so that native tissue is attacked, can result in pulmonary emphysema or acute respiratory distress syndrome.
The naturally occurring human .alpha..sub.1 -antitrypsin has a methionine at the active site for inhibition of many serine proteases, particulary elastase. Oxidation of the methionine to the sulfoxide substantially inactivates the inhibitory activity towards most serine proteases, but not human chymotrypsin.
The ability to inhibit an enzyme, either reversibly or irreversibly, has a wide variety of applications. For therapeutic purposes, the ability to protect a host from the degradative effects of elastase can provide protection from the diseases indicated above. In in vitro systems, there are also uses for inhibition. For example, in diagnostic assays, where one can modulate inhibition in relation to the presence or absence of a ligand, one can use the inhibition for a measurement of the presence or amount of the particular ligand. Furthermore, specific inhibitors can be used for titration of the enzyme, where only a non-specific substrate is available, for isolation and/or purification of an enzyme. Thus, novel enzyme inhibitors can have a wide variety of applications, both in vivo and in vitro.
2. Description of the Prior Art
Partial nucleotide sequences of .alpha..sub.1 -antitrypsin have been reported by Kurachi et al., Proc. Natl. Acad. Sci. USA (1981) 78:6826-6830 and Leicht et al., Nature (1982) 297:655-659. See also Suggs et al., Proc. Natl. Acad. Sci. USA (1981) 78:6613-6617; and Ish-Horowicz and Burke, Nucleic Acids Research (1981) 9:2989-2998. The existence of polymorphisms in .alpha..sub.1 -antitrypsin is reported by Fagerhol and Cox, Adv. Hum. Genet. (1981) 11:1-62. Beatty et al., J. Biol. Chem. (1980) 255:3931-3934, report that oxidation of .alpha..sub.1 -antitrypsin reduces serine protease inhibitory activity. Nakajima et al., ibid (1979) 254:4027-4032 show that a valine derivative is a human leukocyte elastase substrate. Travis and Salvesen, Ann. Rev. Biochem. (1983) 52:655-709, gives a review of .alpha..sub.1 -antitrypsin and its properties. See also copending application Ser. No. 609,540, filed May 11, 1984 abandoned.